In general, an electroconductive resin composition is provided with desired electroconductivity through addition of an electroconductive agent to an insulating binder resin. As the electroconductive agent, there have been known an electronic electroconductive agent such as carbon black or metal powder, and an ionic electroconductive agent such as a quaternary ammonium salt.
The ionic electroconductive agent can uniformly provide electroconductivity to the binder resin as compared to the electronic electroconductive agent of a particle dispersion type typified by carbon black, because the ionic electroconductive agent is uniformly dispersed in the binder resin with ease. In addition, the ionic electroconductive agent causes less coloration of the binder resin, and hence can ensure transparency required for, e.g., a packing material or a protective film for display. However, in some cases, the ionic electroconductive agent present in the binder resin moves toward a surface of the binder resin with the lapse of time, that is, so-called bleeding occurs, resulting in a sticky surface or fouling of a member to be brought into contact. In addition, there is a problem in that the ionic electroconductive agent is ionized into an anion component and a cation component through electrification and moves to be unevenly distributed, resulting in a reduction in electroconductivity.
The ionic electroconductive agent has the above-mentioned shortcomings. However, the ionic electroconductive agent is often used for an electroconductive member for electrophotography by virtue of its feature of being capable of uniformly and stably providing electroconductivity of medium-resistance regions with ease, which is difficult to accomplish by the electronic electroconductive agent. As the electroconductive member for electrophotography to which the ionic electroconductive agent provides electroconductivity, there is given, for example, a charging roller which is arranged so as to be brought into abutment with a photosensitive member and is configured to uniformly charge the photosensitive member.
However, as described above, owing to the problem of the ionic electroconductive agent moving toward the surface, fouling with the ionic electroconductive agent may occur in the photosensitive member to be brought into contact with the charging roller, resulting in an image defect. In addition, in recent years, an electrophotographic image forming apparatus has achieved a higher speed and higher definition, and along with this, the image defect is more liable to occur in association with a reduction in electroconductivity of the charging roller.
Against the foregoing problems, in PTL 1, it is disclosed that a quaternary ammonium salt in which, out of four alkyl groups to be bonded to a nitrogen atom of the quaternary ammonium salt, any one of the groups is an octyl group, and the other three groups are methyl groups is used as the ionic electroconductive agent. When such ionic electroconductive agent is used, the ionic electroconductive agent is less liable to move toward the surface by virtue of its polarity being controlled.
In addition, in PTL 2, it is disclosed that a quaternary ammonium salt having a glycidyl group, which is a reactive functional group, is used as the ionic electroconductive agent. Specifically, the glycidyl group of the quaternary ammonium salt reacts with a functional group present in a binder resin, such as a hydroxyl group, a carboxylic acid group, or an amino group, to form a covalent bond. As a result, the quaternary ammonium salt is fixed in the binder resin, and its movement toward the surface is suppressed. In addition, also a reduction in electroconductivity through electrification is suppressed.